configure finds function, but how to know what to include

This is not really a PHP problem, but I need it for PHP. I'm checking for getaddrinfo using AC_CHECK_FUNCS, the problem is that I don't know where it was found. On one machine it was found by configure in /usr/pkg/include/bind/netdb.h something, while on another it is in /usr/include/netdb.h How can I know where it was found so that I can include the correct file? I either need configure to put the right thing in the Makefile so I can do -Idir, or I need some defines so I can use the right path in #include I can write my own tests to look in a few common places, but there must be a better way. I've been looking through the autoconf manual, but can't see any easy way out. Sorry for bothering the list with this, Stig